text:
How do birds coordinate their turns?
I am building a plane that looks like an Eagle, so I was watching YouTube videos so I can see how to realistically fly it.

One thing I don't understand is how do birds like this coordinate their turns? The bird's tail is flat and flexes a little, but not very much. You can see the wings warping (Wright Brothers style) to go into and out of turns. But with no rudder, it seems like there's both no way to counter the adverse yaw; and with no vertical fin, nothing to bring the tail around while in the steady-state turn.
I was watching the wing tips and have a theory. It appears the inner wing tip feathers are more splayed out than the outer ones. I'm thinking that might increase drag on the inner wing tip, which both counters adverse yaw and brings the nose around during a steady state turn.

There's a book called Miracle Of Flight that covers flight dynamics and mechanics up through the Reynolds Number range, from insects, through birds, to airplanes. Very well written with great photography.

@JohnK Thank you for the pointer! Looks like just the book to add to my frequently re-read books on the Wright Brothers as well as Stick and Rudder.

You might take a look at Prandtl wings, and research by Al Bowers. https://www.youtube.com/watch?v=RoT2upDbdUg

See also comments in chat room for this question -- https://chat.stackexchange.com/rooms/148369/discussion-on-answer-by-deltalima-how-do-birds-coordinate-their-turns

worth reading anything by Adrian Thomas, he's done a lot of research in this area https://www.biology.ox.ac.uk/people/professor-adrian-thomas#tab-2779236

Birds coordinate their turn by rotating their tail along the roll axis. This tilts the lift vector of the tail and makes it work like a rudder.
The roll angle of the bird itself is controlled by wing warping.
You can see this in the video especially when the bird is operating in gliding configuration and the tail is providing positive (upward) lift. During gliding phases, rolling the tail (w.r.t. the body) to inside of the turn reduces slip / increases skid, and rolling to the outside of the turn increases slip / reduces skid). You can see constant small corrections of the tail roll angle, as well as the tail pitch angle to correct for pitch instability.

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You could say that the bird can create half a V tail whenever it needs to.

You might take a look at Prandtl wings, and research by Al Bowers. The lift distribution on most bird wings are different than an most planes. This different lift distribution can mean that the tip of the wing is at such an AoA to actually get a "thrust" out of it -- this is actually what you would see with a winglet. (See 17:54 in the below video.) With the right lift distribution, instead of adverse yaw, you can get proverse yaw.
Birds can warp their wing to customize the effective angle of attack across the wingspan. This is similar to washout on a plane wing, except a bird can change this dynamically in flight. This can be (is) exploited to adjust the drag on each side to cause yaw without a "rudder" -- potentially by causing "thrust" at a wingtip by very heavily "washing out" the wing.
I highly recommend watching the following video of a talk by Al Bowers (NASA researcher) on this topic, he does a much better job of explaining it than I ever could:

Another advantage that birds have over aircraft is pressure (i.e. touch) sensitivity over the whole wing or control surface. They have feeback about the response to small adjustments that a computer or human pilot does not.

Thank you, this is a great video. I did search but didn't find this great video before.

@Liam That's a great point. We have to use gross movements, whereas they can sense the smallest pressure and react with tiny movements that immediately counter it. Much like we manage to stand on our own two feet, so there must be lots of tiny adjustments going on. (A fact that I've become very aware of now that I'm getting older and my coordination isn't quite as good as it used to be!)


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On what basis is the weight unit of the FQIS selected by airlines of various countries?
On what basis is the weight unit of the FQIS (Fuel Quantity Indicating System) selected by airlines of various countries? Does it depend on the local country for using imperial or metric units?

Short answer
There is no mandatory unit, manufacturers are not constrained, customers use a fuel unit consistent with the unit used for other mass data, like gross mass, either kg or lbm.
Fuel mass information is computed from volume sensed by tank probes and fuel density.

Applicable regulation
For US and EU countries and large aircraft:

US: CFR 25.1337.b Fuel quantity indicator says

There must be means to indicate to the flight crewmembers, the quantity, in gallons or equivalent units, of usable fuel in each tank during flight

EASA countries, Certification Specifications, CS 25.1337(b):

There  must  be means  to  indicate  to  the  flight-crew members, the  quantity, in litres, (gallons), or equivalent units [...].

Manufacturer and customer choices
From a manufacturer standpoint:

This is defined at country level, actually at regulator level.
For FAA and EASA regulated countries, as highlighted by @Bianfable, the actual physical quantity to measure is not specified, it can be mass or volume.
For FAA and EASA regulated countries, there are no mandatory units, imperial or international.

This means manufacturers have no constraint on the unit.
What can do airlines:

Use an international mass unit, kg or tonne, since energy is dependent on fuel mass. This is likely the choice for most countries around the world where SI is used for business. This unit will be consistent with other mass data in kg:

A330 ECAM, all masses in kg, source

Use an avoirdupois mass unit, pound-mass (lbm) or long ton, in countries where avoirdupois units are used for business.

A320 ECAM, all masses in lbm, source

Use a units of volume, liter (l) or gallon (gal) as suggested in regulations. This is an unlikely choice for transport aviation as mass is meaningful both for mass/weight and balance calculation and and range determination. So there is little interest in displaying a volume which would need to be converted into mass by the crew.

Converting from volume to mass
Raw data is a volume sensed by capacitive or ultrasonic probes in the tanks. When mass is shown to the crew, it's just a conversion from volume to mass:

This conversion must take into account fuel density. Fuel density for a given type of fuel varies with temperature.
Simpler conversion systems use a standard fuel density of 0.8 kg/l corrected by actual fuel temperature when available.
There is an option to use the actual density measured by an additional densitometer.

As tanks have complex shapes, e.g. to match wing available space, and probes sense a fuel level, volume evaluation is difficult:

The relationship between height and volume depends on the pitch angle ’θ’ and roll angle ‘φ’ of the tank. At present aircraft such as Airbus 320 use look up tables to link height to volume for a set of pitch and roll angles [...] In order to accurately determine the quantity of fuel contained in these tanks large amount of measured data is continuously available as the output of the sensors and interpreted.

For more on this conversion topic, see How is fuel mass measured in airliners?

Mixing units
As mentioned in @busdriver answer, using different units is a source of confusion, and has led to fuel loading errors in the past, with the much talked-about dual engine failure of Air Canada 143:

Canada had just switched from avoirdupois to SI
Newly delivered Boeing 767 had their fuel system set in kg.
AC143 crew ordered fuel in kg.
The refueller computed a volume with a coefficient valid for lbm to l conversion, as it was common at the time.
Half the quantity of fuel was loaded.

The FQIS was not functioning, the error went unnoticed by the crew. Pilots were able to land the Boeing 767 after they ran out of fuel, gliding on a distance of 120 NM.

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In modern airliners this is configuration option that the operator can choose. I don't think there is a requirement on which unit to use, but it would make sense to use the unit that is intuitive to the operators pilots and other staff.
The famous case of mixing kgs and lbs is of course the Gimli Glider.

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What should be approx altitude of jet aircraft 10 nautical miles to landing
Please assume the elevation of airport to 2000ft ASL. Under what conditions ATC might mandate aircrafts to fly at lower altitudes? What might be approximate speed at this distance?

Is this information-gathering for a noise complaint?

Typical landing
Here is a typical landing at Paris CDG with a slope of about 3° (5%).

Jeppesen IFR approach plate, source
Runway altitude is 318ft.

You see the altitude is 3000ft from 10.2NM until a distance of 7.2NM.
Then it follows a radio glideslope at 3° (5%).
Speed entirely depends on aircraft performance. A large airliner may fly at 140kt (A320), but a small GA aircraft may fly at 70kt (Cessna 172).

Minimum altitude
In addition there are obstacles, and there is an indication on the plate: MSA 2000ft within D22.0 PGS. It means the minimum altitude which can be selected by a pilot within a circle of 22NM radius around PGS navaid (located at the airport) is 2000ft. Below this altitude there are obstacles outside of the approach path.
But as commented by @Bianfable, ATC may vector aircraft to speed up the landing, or to separate them. Vectoring means asking them to follow ATC indications instead of using a published procedure. This is not limited to landing aircraft.
In this case the aircraft may be instructed to fly at an altitude below the published one, but above the minimum radar altitude indicated on the first page of the documentation linked, in this case it's also 2000 ft until about the outer marker (OM) where it's 1500ft.

Jeppesen minimum radar alitudes, source

Note your question is difficult to answer as it cannot be assumed the landing is done in straight line, or the initial altitude is 3000ft (other approaches exist at this airport with a value of 4000ft as you'll see if your look at the linked documentation).
It will vary for a specific airport and direction of landing, and neighboring obstacles. A landing in a mountainous area might be different.

That's interesting. Does Jepp commonly publish the Minimum Radar Altitudes around an airport? In the US those are called Minimum Vectoring Altitudes and they are published by the FAA, but with very clear warnings that they are "to be used as a visual reference; they are not to be used as a navigational tool." (And as you mention they are very commonly lower than the published MSA.)

@randomhead, that's not Jeppesen only, the information is published by the French AIP provider (SIA, a State agency), e.g. on their own package, page 35

@randomhead In europe the MVA charts are published and updated regularly with every AIRAC cycle. These charts however are only of an informative nature for pilots as they only refer to ATCOs work. This could be the reason why FAAs public versions are not for navigational use - the ATCOs most probably have the official AIRAC updated versions thereof to vector aircraft

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What is Alpha protection?
This article states:

An occurrence was reported where an Airbus A321 aeroplane encountered a blockage of two Angle Of Attack (AOA) probes during climb, leading to activation of the Alpha Protection (Alpha Prot) while the Mach number increased. The flight crew managed to regain full control and the flight landed uneventfully.

What is Alpha protection?
Is it part of another major system (like auto-pilot)?
What can it do?
How is it activated?

Alpha is also called "Angle of Attack". It is the angle between the relative wind and the chord line of the wing. When the angle of attack is increased to a certain point, the airflow over the wing is no longer smooth. Turbulence is created after the wing, and it loses lift. This is known as a stall.
"Alpha protection" is a system which prevents the angle of attack from getting too high. This is done by software monitoring the plane's angle of attack sensor. When a high alpha situation is detected, the software lowers the nose of the plane to maintain high but still safe angle of attack. It also commands full thrust to all engines. This system is designed to prevent pilots from stalling the aircraft and to allow them to get the best possible performance in emergency e.g. in a wind-shear.
This is not part of the autopilot. It is integrated into the flight control computer and activated at all times. Autopilot are functions which fly the plane in a certain way to reduce the pilot's workload in normal situations (e.g. climb to 13,000 feet, turn left to heading 340).
Pilots can opt to turn off such protection systems should it malfunction, or a very special occasion exists where these protections should be switched off, such as performing at an airshow.

Notable Accidents
In the Airbus, the A320 was the first "fly-by-wire" aircraft. During a demonstration flight AF296 when showing off the alpha-protection system the pilots took the airplane too low and too slow and disabled the part of the system that should have commanded full thrust. The plane didn't stall but was having too little energy to climb anyway. It crashed gently into the trees.
In an acceptance flight, the pilots were testing the alpha-protection at low altitude. The system should have prevented the plane from pitching too high. However, to the surprise of the crew, it failed. The plane stalled with insufficient altitude to recover. The system did not work because water got into the angle-of-attack probes during previous improper washing procedure, froze during the flight and blocked the probes.
In AF447, the system switched to "alternate law" and no longer provided stall protection, because the pitot tubes (airspeed sensors) froze over. The plane stalled from 38,000 feet to the water after the pilots failed to apply correct procedure for unreliable airspeed.

Re final para: For AF296 the alpha protection prevented a stall, but by then the aircraft was too low and too slow to clear the trees ahead. The pilot claimed the engines did not respond and that the altimeter was incorrect, so far as I know he didn't blame the crash on alpha protection.

For XL888T the problem was a frozen AoA sensor that had earlier been improperly washed with a pressure washer. This became an issue when the pilots carried out unauthorised and improvised testing at low level.

@RedGrittyBrick re AF396: from what I recall from the documentary, the pilot claimed that when he pulled back on the stick, it pitched down. XL888T: Yup the sensor was frozen, so the system (as a whole) failed.

I've not seen where Michel Asseline claimed that and the video footage doesn't show any pitching-down  https://www.youtube.com/watch?v=-cv2ud1339E. Of course, as the aft of the fuselage is dragged through the trees it must eventually affect aircraft attitude. That's not alpha protection.

AF296 is notable by two things: That the Alpha protection saved all but three people on board and that overconfidence in technology causes accidents. They were trying to demonstrate alpha protection, but they've exceeded it's capabilities. If it didn't activate, the crash would have been worse. Also note, that they manually deactivated the other bit that commands full throttle. If they didn't, they would have made it, because the engines would have spooled up earlier.

The main motivation behind the alpha protection system are actually accidents like Delta Airlines flight 191 that were caused by windshear. In those cases the pilots need to get as much lift as they can get and that's what the system lets them do reliably.

@JanHudec I always thought the impact of that accident is better understanding of wind shear and development of wind shear alert systems.

The angle of attack is not always measured relative to the wing chord line. If you're working with isolated cambered airfoils (i.e., not part of an aircraft), the zero-lift line is often used in lieu of the chord; similarly the zero-lift line of an aircraft is sometimes used as the datum (so zero alpha -> zero lift).

@kevin: That too, of course. But alpha protection too. It allows pilots maintain highest safe angle of attack and therefore loose as little altitude as physically possible and it also commands maximum thrust if the pilots did not do it already.

"the pilots failed to apply correct procedure for unreliable airspeed." This is a good candidate for 'aviation understatement of the century.' The pilots failed to apply correct procedure for flying an airplane.

Also, another notable incident regarding alpha protection is with TC-JDN on a Turkish Airlines flight from Istanbul to New York. In this incident, turbulence caused the AoA to briefly reach the point at which alpha protection is activated. Apparently the alpha protection mode holds the aircraft at the 'alpha prot' AoA until a nose-down command is given on the sidestick. This resulted in an uncommanded climb and a near-miss with an A330 that was above it over the Atlantic.

@reirab thx for the link. I find it ridiculous that the Airbus "protection" systems kept the aircraft in an undesired climb...

@kevin better be in undesired climb than undesired fall due to stall. Also note that knowledge of those protections and how it works are teach in training.

Alpha protection is a safety measure that prevents an airplane going over certain values of angle of attack. Usually "alpha" is used to designate the angle of attack.
When an airplane is flying, if it exceeds a certain value of angle of attack it will enter a stall (less lift, sometimes suddenly, and the plane falls like a rock). Airbus introduced this safety check into the flight control system that blocks the airplane from getting closer to dangerous values.
Anyhow pilots are able to recover from a stall.
So alpha protection is just software on board.

Not all aircraft fall "like a rock" when stalling. Some just pitch gently down and resume flight, others mush along with a higher but stable sink rate. Only bad designs will show nasty stall characteristics, and, unfortunately, those have been built, too.

"Falling like a rock" is not the same as having "the aerodynamics of a rock". I tried to express with falling that the gravity is only partially compensated by lift, not saying that the post-stall behaviour of the airplane is the same behaviour as a rock. This behaviour of falling can be felt actually by people when airplane is affected by gust, where the AoA seen by airplane really varies suddently. Screaming is a good way to measure it :)

@TrebiaProject. That's usually a downdraft, not a sudden loss of lift. The wings are still producing lift, but the whole air mass is moving downward, pushing the plane down along with it.

And then there's the Ercoupe...

@Trebia Peoject  let's compare stall recovery of a paper airplane to a 737.  The issue is weight to surface area.  This affects altitude loss in the event of a stall.  A paper airplane recovers in inches, the larger plane needs several thousand feet.  Really comparing a goldfish to a whale.  So massive planes must AVOID stall.  Higher efficiency wings (higher AR) wings will stall at a lower AOA compared with older designs.  Pilots must be properly trained.  Alpha protection is needed.  But I would definitely look into beefing up those slats.

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How could I match the surrounding traffics displayed with their radio communication
If I have a traffic display I could see the traffics in proximity of my aircraft and meanwhile I could listen to their voice communication. So how could I match the traffic shown in the display with the corresponding voice communication? My understanding is that if I have a ADS B in system and the other aircrafts have mode-s transponder, I could know their call sign thru the ADS-B data, is that right? But how about I just have a TCAS or I have the ADS-B in transponder but other aircrafts do not have a Mode-S transponder?

IANAP, but shouldn't all radio communication start with <who I am> and <who I'm talking to> (maybe in the other order)? If you hear someone say N12345 on approach runway 17L, you should be able to correlate N12345 with the appropriately labeled blip on your traffic display, no?

I could correlate N12345 to the traffic on my display who is indicated as approaching RW17L, but I can not be 100% sure, right? N12345 could be a aircraft without transponder, that is not shown on my traffic display or I have 2 traffics displayed as on the approach and I still can not tell which one is N12345, please correct me.

Several approaches, currently impractical for GA:

Your radio receiver would need to be directional, to estimate the
sender's bearing and maybe distance, and from that derive the
sender's identity.
Voice broadcasts would need to be augmented with a digital squawk
indicating the sender's call sign, like some automated speech
broadcast weather reports do.
Onboard automatic speech
recognition
trained particularly for call signs could try to infer the sender's.

But we're a long way from duplicating how videoconfering software highlights whoever's speaking.


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Is an aileron roll easier, opposite the rotation of the propeller?
We all know helicopters have tail rotors because they would spin out of control thanks to Newton's third law.
That got me thinking, would a single propeller plane have an easier time doing an aileron roll opposite the rotation of the propeller? And do light aircraft require any special tricks like having one wing longer than the other or the ailerons being tilted in the rest position?

A failing tail rotor is a recoverable failure in a helicopter given the right conditions.

Yes.  In the US, props spin clockwise from the pilots point of view, so rolling left is easier than rolling right.  No tricks on the wings. Ailerons might have small trim tabs that are adjusted for straight & level flight.

Some aircraft do have an offset thrust line to counter propeller turning effects.

I question the answers presented here. When the engineers design the aircraft, they take into consideration the effect of the rotating propeller. If they didn't the pilot would have to constantly provide offsetting flight control inputs to keep the wings level (to prevent a roll). So the amount of aileron required (and the resultant lateral trim forces) should be the same for rolls in either direction.

Another technique used on some aircraft is to mount the wings at slightly different angles (of incidence)) to compensate. Aircraft so modified would require identical trim forces to generate rolls in either direction.

Yes: Rolling one direction easier than the other, as you mentioned, newton's laws are at work here.
Special Tricks? Also Yes.  There are several design strategies to deal with asymmetries of thrust from propellers.  Bear in mind that these thrust asymmetries are not always at work, so any design feature is a trade off.  The propeller must be running, angle of attack is a factor, etc.  I have heard of asymmetrical wing incidence used, but more often a slight offset of a tail-plane, such as the vertical stabilizer is used.

I question the answer presented here. As mentioned, when engineers design the aircraft, they take into consideration the effect of the rotating propeller. If they didn't, the pilot would have to constantly provide offsetting flight control inputs to keep the wings level, depending on other factors such as AOOA, power setting etc. So the amount of aileron required (and the resultant lateral trim forces) should be the same for rolls in either direction.

@CharlesBretana because prop torque is variable with rpm and pitch, it would be very difficult to develop a passive system to cover all bases.  This is why rudder must be applied in high power/slower flight situations.  Generally, it is easier to roll one way than the other with a single engine.  (PS way safer to use the rudder).

@Robert, Yes, I understand that, but obviously, if designers make an adjustment to compensate for a part of the effect generated by prop torque, then isn't it indeterminate (at any specific rpm, AOA, and pitch attitude) as to what direction would be easier to roll? Isn't it clear that at one end of the rpm/AOA spectrum it will be easier to roll in the direction opposite from the direction that would be easiest at the other end of the spectrum?

... and rudder is only effective at higher AOA, where adverse yaw exists. It is not slower (airspeed), that matters. Rudder at low AOA, at any airspeed, only generates a sideslip. Secondly, High power settings cause P-Factor yaw because of AOA, (the angle between the plane of the prop and the relative airstream), The other yaw-inducing effect is from the corkscrew (helical) shape of the prop wash hitting the vertical stabilizer. But this yaw (sideslip) only induces a roll when at significant AOA.

@CharlesBretana I'm unclear on which part of the answer you are questioning.  Is it whether the roll is easier in one direction vs. the other, or about the compensation in the design?

My apologies, I am questioning whether the roll would be measurably easier in one direction or the other, when, knowing about the effects of torque, P-Factor, and the like, aircraft designers include compensating design elements to eliminate or mitigate these effects in this flight regimes where it would be a significant issue. The upshot, I would surmise, is that across the wide spectrum of flight conditions, in some of them, rolls would be easier in one direction, whereas in others the opposite would be true.

I think it is likely that we focus on the ones where the known effect is most significant, (like high Power (torque) takeoff rolls), simply because they are the scenarios where the effect is most likely to cause a problem.

Analogously, I would argue, (for the same reason), that a statement that a helicopter can yaw much easier in the direction that the main rotor is spinning than in the opposite direction, is incorrect.

Yes.  Even more yes when the engine also has a lot of rotating mass, as with the Sopwith Camel.  "The torque effect of the engine also meant that the aircraft rolled much more readily to the right than the left and this could lead to a spin. Many novice Camel pilots were killed when they turned right soon after take-off."  https://www.warhistoryonline.com/world-war-i/the-killer-camel-sopwith-camel.html


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Which is better: a rotor / prop followed by a stator, or contra rotating rotors / props?
It is all in the title.
I'm interested in power absorbed/used for a given thrust, or thrust generated for a given power (same diameters of course).
Just thrust and power.  Ignore materials, electric vs turbine, complexity of the  contra-rotating mechanism, etc.

Undisturbed inlet flow provides the highest efficiency.

The single rotor with stator has a straightforward inflow; outflow will have a tangential component which is lost for thrust generation. The stator will bend the outflow back in the axial direction, but there still remain pressure increases with blade passing frequency.
The contra rotating rotor has one of the rotors in the disturbed flow of the first rotor - this second rotor will therefore have lower efficiency in transforming engine power into thrust.


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What is this little strake on Cessna 182 vertical tail?
What is the reason of mounting this little horizontal strake on a Cessna 182 vertical tail?

All the irrelevant things I notice: A) why didn't they move their logo just a little forward on the tail so it doesn't run into the vortex generators? B) Why is there a car and a motor home parked in the hangar? C) Who has a garage on their house big enough to hold a 182 and a car and a motor home???

@FreeMan Re. B and C, can we assume you don't live in the US? :)

It is a VOR antenna. See also: https://aviation.stackexchange.com/q/67237/8749, https://aviation.stackexchange.com/q/50120/8749, https://aviation.stackexchange.com/q/38218/8749

Au contraire, @Pondlife, I do. I've seen garages for motor homes, but I don't know that I've ever seen one attached to a house that was large enough to hanger a small aircraft. Also, since IANAP, is parking road vehicles inside the hangar a "normal" thing? (I suppose if it's a private hangar you can park whatever you want in there...)

I didn't even thought about that. Thank you!

Duplicate of https://aviation.stackexchange.com/questions/67237/what-is-this-flat-plate-sticking-out-of-the-tail-of-learjet-24d? ?  At least the answer is the same--

@FreeMan Google "airpark communities" for a sense of what's out there. It's pretty common to keep road vehicles, boats etc. in privately owned hangars. Airports usually have an "aviation use only" clause in hangar rental contacts but they're often ignored.

@FreeMan Believe it or not: in Germany we have a garage regulation that only allows for storing items in a garage which are related to the car (and of course, a car itself). You may store winter tyres or a roof box but not a lawn mower or an old couch. :-) On the other hand, there's a German idiom which translates to "no plaintiff, no judge." Dunno if that is known/common in English.

@PerlDuck Based on the stereotypes about Germans being neat, tidy, organized, and punctual I would absolutely believe that! Of course, stereotypes are based in fact, even if they become extremely exaggerated... :)

@PerlDuck Our version is "it's only illegal if you get caught." In this case, as long as you actually have a plane in the hangar, airport authorities generally don't care what else you have in there. It's quite common to drive to your hangar and leave your car inside while you fly. They just want to stop folks from using them solely as storage units (or living space).

@FreeMan This is obviously a hangar, not a garage. Some people build their house (apartment) in their hanger :)

It's one half of a VOR receiver antenna. There will be a corresponding element on the otherside of the tail.
The complete unit looks like this:

Source
Disclaimer: I have no affiliation with the the company from whom I borrowed the image - it was just a good image to illustrate the point.


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Could ballonets be used in rigid airships
Ballonets are used to maintain the shape of non-rigid airships, and as buoyancy compensation.
Could ballonets also be used for buoyancy compensation in a rigid airship?
I'm wondering if a ballonet system could be used for limited height-control in a story I'm writing.

Yes, inflating ballonets in an airship's rigid envelope would necessarily compress the "gasbags" therein containing lifting gas, thereby increasing that gas's density and reducing the airship's buoyancy.
However, the extra pressure that this would impose on the gasbag skin would demand a stronger and thus heavier skin.  The extra weight of both the skin and the ballonets themselves might not justify their use.  So your guess of limited height control is justified:  squish the gasbags only a few per cent, with ballonets so light and flimsy that they often break (which is no cause for alarm).

Could a balonet be placed in each, or some of, the individual cells? These would have to be heavier, to withstand pressure, of course.

Ah -- reinforcing several gas-bags will quickly increase weight as much as reinforcing the outer envelope; having multiple balonets and inflating systems will add more weight, and we're in the same position as before... I think.


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How can one estimate wave drag?
Wave drag is an especially high drag above mach 1, but I've found it hard to find source materials to estimate it. I'm looking to estimate how to design better for wave drag by estimating how it would affect my flight in the transonic region Mach 0.8 - 1.2.

Welcome to Aviation.SE. Speeds up to Mach 1 are subsonic by definition and do not have wave drag. You might want to simplify your question to focus on one aspect. It requires several answers in its current form, and this site tends to like one at a time.

Hey @Pilothead, thanks for the heads up. Thanks for welcoming me , and I have simplified the question and perhaps I'll add the other elements in another question.

@Pilothead As you increase speeds past about Mach 0.6 you enter the transonic regime where areas over which flow acceleration occurs (such as wings) may encounter sonic or supersonic flow

Usually wave drag $c_{d_w}$ starts becoming relevant at the drag divergence Mach number $M_{DD}$, which is defined as
$$\left.\frac{\partial c_{d_w}}{ \partial M}\right\vert_{M=M_{DD}}=0.1 \tag{1}$$
Or in words, the Mach number at which the wave drag coefficient versus M has a gradient of 0.1
Lock$^1$ has derived an empirical formula that shows the development of $c_{d_w}$ after the critical Mach number, $M_{cr}$, which is the number at which the flow becomes locally supersonic on the wing:
$$c_{d_w} = 20(M-M_{cr})^4 \tag{2}$$
If we apply the definition of $(1)$ to $(2)$ we obtain:
$$M_{cr} = M_{DD} - \left(\frac{0.1}{80}\right)^{1/3} \tag{3}$$
As you can see, the value of $M_{DD}$, is a little bit higher than the value of $M_{cr}$. First you get local super sonic flow, but the drag does not increase rapidly, as you further increase the Mach number, the drag starts to increase significantly, and you reach $M_{DD}$. See this image, where $M_{DD}$ is denoted by $M_{CDR}$.

Source
The value of $M_{DD}$ can be estimated using:
$$ M_{DD} = \frac{K_A}{cos \Lambda} - \frac{t/c}{cos^2 \Lambda} -\frac{c_l}{10cos ^3\Lambda} \tag{4}$$
With

$\Lambda$ is the sweep angle
$t/c$ the relative thickness of the section lift coefficient
$c_l$ the section lift coefficient
$K_A$ the airfoil technology factor (a correction factor denoting the quality of the airfoil). Typical values for the airfoil technology factor are 0.87 for an NACA 6-series airfoil section or 0.95 for a supercritical section.

So the workflow is as follows:

Estimate $M_{DD}$ using $(4)$
Derive $M_{cr}$ using $(3)$
Determine the development of $c_{d_w}$ using $(2)$.

For more info, see this link and this link
$^1$ Hilton, W.F., High Speed Aerodynamics, Longmans, Green & Co., London, 1952, pp. 47-49
Note, this method is only for estimating the wave drag coefficient around the drag divergence Mach number, I'm not sure to what Mach number it provides an accurate estimate

thanks a lot for all the formulae and the info. You've been super helpful and I will look into the book as well.

@RajathPai You're welcome. As you can see your question has been 'on hold', because it's a very broad question. As such, other people can not answer to it anymore. Very broad questions are difficult to answer, please focus on one question per post. You can edit the question to make it more specific and then it can be reopened again. If you have any other doubts concerning how to improve your question let me know. If you want to ask another (different) question on an aviation topic, please make a new post.

I already edited it and reduced it once. I will try to reword it and be more specific. Thank you for your advice.

I think the second and third terms in equation 4 should have negative signs on them, increasing thickness decreases divergence Mach no, as in Korn’s relation

@AlastairWyllie well spotted, I've edited it.

I'm sorry to be a nuisance, but should the third term be divided by 10? as in 10cos^3(lambda) on the bottom? Also, thank you, this is extremely useful, and is helping me no end with my own calculations

@AlastairWyllie, again correct. Apparently I'm very bad at copying formulae from my own thesis :)

@AlastairWyllie This is Dave Korn's formula for airfoil wave drag extended to the swept wing by W.H. Mason. The "10" can actually be anything between 7 and 10 to best match experimental results.

Interesting! Thank you!

@PeterKämpf do you know where I can find the original paper on this equation, I can't seem to find it and I'm kinda interested to see the derivation

@AlastairWyllie There isn't much of a derivation. As Mason writes in ConfigAeroTransonics.pdf: "It is based on “the Korn equation,” which was an empirical relation developed by Dave Korn at the NYU Courant Institute in the early 1970s, and in use at Grumman when I arrived in 1974"

Ah okay, Thanks anyway!


text:
What does the “nose-high” product of inertia represent?
I am reading this slide:

Source: http://www.stengel.mycpanel.princeton.edu/MAE331Lecture10.pdf
Is Izx always considered small and we can assume it is 0, as many texts assume?
I need to make this clear:
This is the body axis:

I assume that G is the center of mass, GZX is the symmetry plane. So  Iyz = Iyx = 0. But why is Ixz zero? Do they rotate the body coordinate system around Y axis so that Ixz = 0?

I think you may get a quick and straight answer by emailing the lecturer (just a suggestion, nothing against your question)

This is an addendum to @ROIMaison's answer based on the modified OP.

I assume that G is the center of mass, GZX is the symmetry plane. So Iyz = Iyx = 0. But why is Ixz zero? Do they rotate the body coordinate system around Y axis so that Ixz = 0?

The coordinate axes are completely arbitrary. By convention, the x-axis aligns on the symmetry plane and points from nose to tail. However, one can choose literally any orientation. You can, of course, align the axes such that all the cross inertial products are zero; such axes would be the principle axes. But obviously this would only work for a single configuration, fuel distribution, etc.
To answer your question more succinctly, no, we don't change the axis once the initial drawings are made. The coordinate system stays fixed and becomes the body axis. For a conventional design, the cross products would be fairly small and would not be a big deal to ignore for first order flight dynamics analysis.
What would happen if you align the axes weirdly such that the cross products are all large and non-zero? Nothing really, it just complicates your math and modeling, and your angular velocity $[p,q,r]$ would be hella confusing. But physics would work out just right.

so your answer is that: Ixz is small so we can set it to be zero. What about the author idea of nose high/low product of inertia ? What does that mean?

Nose tilted higher (nose-high) than the x-axis, or nose tilted lower (nose-low) than the x-axis, produces cross inertial product. Simple as that.

that is so obvious, that confuses me why the author said such obvious thing

It's a name given by the author for Ixz.

wow that makes sense to me now

Physics does not care what coordinate orientation you choose to use. You might find easier to invert a diagonal 3×3 matrix by hand, but as far as computations go it makes little different nowadays.

The $I_{xz}$ moment of inertia is a measure for how the weight is distributed in the xz plane.
You can obtain it by multiplying a unit of mass $dm$ by its distance in $x$ and $z$ from the center of gravity and taking the negative of it.
For discrete masses (blocks of mass) it looks like this:
$$ I_{xz} = \{-(x_1 \cdot z_1) \cdot m_1\} + \{-(x_2 \cdot z_2) \cdot m_2 \} + \{-(x_3 \cdot z_3) \cdot m_3 \} ... $$
If you look at the plane in question, you can see that it has a nose - which we can consider as one of the blocks - which is

Far in front of the c.o.g. (large value of $x$)
High up from the c.o.g. (large value of $z$)

If we plug this in the formula, we see it leads to large values of $I_{xz}$.
Similarly, there is also a lot of mass in the lower-right corner

Far behind the c.o.g. (large  negative value of $x$)
Low below the c.o.g. (large negative value of $z$)

In essence, everything that is on the x-z line contributes to this value, and as we see from the marked area in the image of the Valkyrie, there is a lot of mass around this line.
If your aircraft is symmetrical around the x or z axis (in terms of as much mass above/below front/aft the axis) you will get a low value of $I_{xz}$.
I guess that is the case for many aircraft, so they make the assumption of $I_{xz}=0$.
More information about the rotational moment of inertia can be found here.

To be more precise, if the aircraft is symmetrical about x OR z axis, the cross product will be zero.

Ah good catch, I will change it, thanks!

Would the anonymous downvoter care to elaborate?

if we have a block that has large value of x and large value of z, and a block that has large negative value of x and large negative value of z then the total of them would be larger, they do not cancel out each other like the idea in the answer. Please explain this point further

@Dat In the answer, I mention that geometries that are symmetrical around $x$ or $z$ have $I_{xz}=0$.  The case in your comment is neither

Did you mean if the geometrie that are nearly symmetrical then we could have Ixz
is nearly zero ? But what does it do to high nose and low mass in the back ? I don't see that help to minimize Ixy

High nose and low mass in the back both add to $I_{xz}$ thus making it larger, if you have a nearly symmetrical plane around the x or z axis (thus no high nose etc.), you will have a low $I_{xz}$. I didn't mention $I_{xy}$

My answer got downvoted as well for no apparent reason. Just ignore the trolls.

@ROIMaison I understand that if I have a nearly symmertrical plane around the x or z axis, I will have a low Ixz. But I don't understand what is the point of the "high nose"? What idea did the author want to convey?

@Dat Not sure how else to improve upon ROIMaison's explanation above...Nose higher than the body x-axis, and you have higher Ixz.

@Jimmy I know and understand the formula to calculate Ixz very well. So what is the meaning of that part: "far in front of cg, high up from..far behind ..low below.." I just can't get it

@Dat, if you know how to calculate the $I_{xz}$, you can just calculate the $I_{xz}$ in a simple way, using some blocks for the wings/tail etc for two planes, one with a normal nose and one with a high nose, and compare the two values.

@ROIMaison so higher nose give us larger Ixz, that's so obivous. So what does the author of the text want to say?

If you want a definitive answer on that you should ask the author. I think he wants to say the arrangement of components (such as the nose) have an influence on the value of $I_{xz}$ and thus on the rotational characteristics.

@ROIMaison I added some information in the post, please check it again

Note that the inertias are defined in the body axis system. Not all the main inertial axes are aligned with the body axis system: The high nose section and the low engines combine to tilt the inertial X axis nose-high. This requires a correction term in the inertial matrix, namely the I$_{xz}$ term.
If, say, the left wing would be heavier than the right wing and the right canard much heavier than the left canard, there would be an additional, nonzero I$_{xy}$ term. Due to the left-right symmetry this term is also zero for the XB-70. More generally, if the aircraft mass distribution can be represented by the sketch below, the cross-coupling terms (those with unequal indices) are nonzero.

Unequal mass distribution: The long rod represents the fuselage with its X-axis (dot and dash line) while the cg symbol represents an additional mass mounted at a distance from the X-axis. Without that additional mass, or if the mass would be at the center of the rod, the I$_{xz}$ term would be zero indeed. You need both: Distance in X and in Z for it to add I$_{xz}$.
Now imagine the arrangement above is rotating around the X-axis: The centrifugal force on the additional mass will add a strong pitching moment, pulling the arrangement into a vertical orientation. This does not happen without that extra mass or without a lever arm of that mass in X direction.
Most aircraft don't have this misalignment between body and inertial X-axes, so for them it is correct to set I$_{xz}$ to zero. Notable exceptions are the Douglas X-3 and a range of McDonnell-Douglas aircraft like the F-101 Voodoo and the F-4 Phantom II: Here the inertial x-axis was pointing down relative to the body axis and artificial stability augmentation had to be added to avoid roll inertia coupling.

Ixz is generally small compared to the other principle inertial terms, and are ignored for first order studies. But it is never actually zero unless you have a flying saucer.

@Jimmy: Aviation is engineering, so close enough to zero is zero. Also please note that I never said that I$_{xz}$ is zero, that is only your interpretation.

@PeterKämpf: I always assume all aircrafts are symmetrical around xz plane so for me, Ixy is always zero (no doubt). Why did you metion Ixy here? I don't get your point. All I want to know is why Izx = 0 ?

@Dat: I added an example in a different plane, that is all. Sorry if this confuses the matter more than it helps. I added more on the xz asymmetry - let me know if this is more helpful or not.

@PeterKämpf I added some information in the post above about where I am stuck


text:
Why are airliner seats higher than chairs and couches at home?
I'm 6-feet tall and even I find airplane seats too high. My feet barely touch the ground when I sit upright. Why can't they make the seat cushion as low as a living room couch?

What aircraft are you asking about? Most of the aircraft I have flown have adjustable seats, and some sit very low to the floor of the aircraft regardless of how much you adjust them.

Which seats are you asking about? The pilot seats, or the passenger seats?

I was referring to the passenger seats :P To a layman, it appears if they make it lower like car seats, it wouldn't sacrifice safety, and it would be more comfortable for short people. It's not good for blood flow when the feet cannot touch the ground. I find it more comfortable sitting in a car seat for a few hours vs. sitting in an airplane seat.

Because your couch doesn't have an ejection charge installed underneath it, while your airliner seat does.  (Didn't you know?)

I also imagine you might find there's a considerable difference between the seats in first class and those in coach :-)

Storage.
You don't have someone sitting behind your couch trying to shove their luggage under it.

The short answer,
Your couch is made for you to fall asleep on, watch football from, and generally be of any non determinant shape since no couch (as far as I know) carries a type certificate.
Aircraft seats are designed to fit as many passengers as is legally allowed and practically possible while still passing the 16G tests the FAA imposes. The 16G requirement is largely for your safety.
Most pilot seats are in some way adjustable up/down and forward/back depending on the age of your aircraft.


text:
Aircraft continuously circling before landing (not holding)
On Flightradar24 I saw an Airbus 320 circling a lot before landing.
My best guess is for some reason the aircraft had to stay in air for longer time due to unknown reasons. If this is the case, why didn't it enter a holding pattern or take longer vectors instead?

We can exclude two possible causes:

doing relay for the Tour de France https://twitter.com/flightradar24/status/1304072106947289088?lang=de
showing passengers the northern lights https://www.news.com.au/travel/travel-advice/flights/easyjet-pilots-perform-midair-uturn-so-passengers-can-see-northern-lights/news-story/171e0fceb915f192dd1d5ea4fb8846bc
There you go, 2 possible reasons less ;) !

These would help us answer, whatever you can find:    What is the scale on that map?  Which day, time (and time zone)?  What weather there and then (was it just drifting with the wind, with steady bank and airspeed for comfort)?  What other traffic there and then (busy runways or gates)?  Any https://en.wikipedia.org/wiki/NOTAM?

(As you're new here, Dev, in case it's not obvious, to reply, please don't add more comments like this one, but instead edit your question.  Great first question, btw.)

FYI circling is another thing: https://skybrary.aero/articles/circling-approach. What we see is closer to orbiting.

This is very odd - a new user asks a question and it's answered by 2 more new users...

@SteliosAdamantidis I found no authoritative technical use of "orbiting" for airplanes.  If "circling" is misleading here, a better term might be "loitering."

Clearly it's for spraying chemtrails. How else are they going to be sprayed. They're not going to spray themselves.

There could be multiple reasons for an aircraft to be doing such circling.

The airline might be conducting some flying training (yes, a costly affair when you can do the same on a simulator)
They could be doing some test flying on that aircraft to evaluate something.
They were put on a hold but not over the usual holding point for Kolkotta.
It could even be due to some blockage on the runway that required the ATC to place the incoming flight on a loose hold but not over any specific point.

Unless we know the specifics it is difficult to give a particular reason.

The 4th point is a good one.

Too much altitude or time. In rare cases an aircraft will have too much fuel to land. I suspect they had time to kill and not enough room to do it.

You wouldn’t hold like that though, you would set up a hold in the airbus flight management system and it would hold an exact holding pattern in space - not drifting to the south east in circles!


text:
Do you have to fly to an airport with an instructor before you can solo there?
I am currently doing my flight training and my CFI said that before I can fly solo to another airport he needs to fly with me there first. Is this true?

Short answer:
Your instructor is correct, if the airport is less than 50 miles away, or is in class B airspace. If it's more than 50 miles away then you don't need to fly there together first.

Long answer:
It depends on the solo endorsement that your instructor plans to give you. There are two sections of regulations that apply to student solos to other airports, in 14 CFR 61.93. Your instructor is probably talking about the requirements in 61.93(b) that apply to solo flights of less than 25 or 50 miles.
61.93(b)(1) says (emphasis mine):

(1) Solo flights may be made to another airport that is within 25
nautical miles from the airport where the student pilot normally
receives training, provided -
(i) An authorized instructor has given the student pilot flight
training at the other airport, and that training includes flight in
both directions over the route, entering and exiting the traffic
pattern, and takeoffs and landings at the other airport;

61.93(b)(2) says (emphasis mine):

(2) Repeated specific solo cross-country flights may be made to
another airport that is within 50 nautical miles of the airport from
which the flight originated, provided -
(i) The authorized instructor has given the student flight training in
both directions over the route, including entering and exiting the
traffic patterns, takeoffs, and landings at the airports to be used;

But, for a solo flight that takes you 50 miles or more away from your home base only the general requirements in 61.93(a) and (c) apply. They don't state that the instructor has to give you flight training at the destination. That would apply to your 150 mile solo cross country, for example.
Additionally, 61.95(b)(1) requires training at an airport in class B before a student can fly there (emphasis mine):

(b) A student pilot may not operate an aircraft on a solo flight to,
from, or at an airport located within Class B airspace pursuant to §
91.131(b) of this chapter unless:
(1) The student pilot has received both ground and flight training
from an instructor authorized to provide training to operate at that
airport, and the flight and ground training has been received at the
specific airport for which the solo flight is authorized;

Having said all that, 61.93(a)(2)(iv) allows an instructor to put any conditions they like on a cross country endorsement:

Comply with any limitations included in the authorized instructor's
endorsement that are required by paragraph (c) of this section.

It's possible that your instructor wants to limit you to airports that you've already flown to together, either for his own comfort level or for owner/insurance reasons.
I suggest you ask your instructor to talk through the various solo endorsements with you and explain which ones he'll provide and when.

I had one CFI that limited solo XC to airports I’d previously visited with him, and another CFI (same school!) who believed the point of a solo XC was going places I hadn’t been to before. Both positions are understandable, and the FARs don’t rule out either.


text:
What can you do with an ATP that you can’t with an R-ATP?
So I know about the different requirements for an ATP vs R-ATP but I can’t find what you are able to do with a full ATP that you can’t do with an R-ATP

All of the limitations of an R-ATP can be found in 14 CFR 61.167, Airline transport pilot privileges and limitations:

(b) Limitations. A person who holds an airline transport pilot certificate and has not satisfied the age requirement of § 61.153(a)(1) and the aeronautical experience requirements of § 61.159 may not:
(1) Act as pilot in command in operations conducted under part 121, § 91.1053(a)(2)(i), or § 135.243(a)(1) of this chapter, or
(2) Serve as second in command in flag or supplemental operations in part 121 of this chapter requiring three or more pilots.


text:
How to calculate runway length required for an A380 to takeoff?
I was wondering, how much runway length does an Airbus A380 require to takeoff? I saw other answers on Aviation S.E. but I didn't find how to calculate it to (I am curious to know how to calculate it). Can someone please help me with this?

Does this answer your question?

For any aircraft, calculating the TODR (take-off distance required), requires the pressure height of the aerodrome, shade temperature, runway surface, wind, wind direction, aircraft weight.


text:
Does the pilot always need to use stick to compensate roll caused by pedal?
When the pilot uses pedal in a fighter like F-18, does the aircraft roll? If so, is it the pilot's job to compensate this roll or the control system compensates it automatically? In other words, is it always necessary to use stick with pedal or the pilot can use pedal without any stick?

Not always. Part of the motivation for FBW is to decouple the controls.

What do you mean by "compensate"?  Prevent roll to achieve unbalanced flight?  You might want to clarify, because necessity depends on what you are trying to achieve.

My premise is that the FBW controller should control the plane such that the rudder pedal produces pure yaw. Is my premise wrong?

Depends on the airplane, but normally there is some roll rate generated by yaw, so, yes, to some degree or another. It's called Roll/Yaw Couple, and sometimes, "secondary effect of controls".
Swept wing airplanes, or airplanes with extreme dihedral angles, will generate pretty hard roll rates from yaw; straight wing airplanes less so.
You would have to find someone with actual F-18 flying time to know how hard it rolls when yawed (hard to say how well the DCS F-18 simulates it), but lets assume it rolls moderately hard with rudder input, and the Fly By Wire system in the plane lets you do it.
If you didn't want it to roll as you yawed it, you would do what you do with most airplanes, apply opposite aileron to prevent the roll, and you'd fly along skewed sideways with, say, left rudder and right aileron.  If you just keep the wings level, it will change heading into the yaw, doing a flat turn, and it will take some additional aileron to create an opposite bank angle as well, if you don't want it to turn.
If the plane has a mild roll/yaw couple, as my Pazmany PL-2 has, you can point the nose off to the side with rudder, and it will only slowly roll in the direction of the skid, and you can prevent the roll with a very light aileron input, with a bit of opposite bank included if you didn't want it to change heading.
Just why you would use pedal alone to yaw an F-18 in the first place, that's another question.  Pointing the cannon at things that are off-axis?


text:
what is considered a good pedal performance in a fighter?
What is considered a good performance in designing the directional control law in a fighter? Is it acceptable to have some roll when using a pedal? For example, is it acceptable to have 40 degrees roll when using a full pedal?

I think it's more about roll rate (or moment).

And duration.  40 degrees in a second is excessive, but not after a minute.  And how do you define “good”?  Performance on par with a non-computer controlled aircraft would be my starting point, fine tune it from there based on test pilot feedback.

Re  "For example, is it acceptable to have 40 degrees roll when using a full pedal?" -- on an aircraft with non-computerized flight controls, if you held full rudder deflection (w/ no counteracting roll control aileron input) you'd expect (to a loose approximation) to see a constant roll rate, not a constant bank ("roll") angle.  What that roll rate would be, at any given airspeed, would be depend tremendously on the shape of the particular aircraft.  The question could use some improvement to address this issue.

And as for computerized control laws?  It's hard to see why you would allow (deem acceptable) any significant roll rate in response to rudder input.  But again the question is best framed in terms of roll rate, not roll/bank angle.  Again, the question could use some improvement to address this issue.

My question is about the computerized control case. I understand from your response that the roll rate is important. So, How much roll rate is considered a good performance if you use full pedal. In other words, how much can it be at most that you describe the control law as a good one? Is there any reference? Is there any rule of thumb?


text:
Is any of the Ingenuity helicopter's special design attributes helpful in improving helicopters flying in Earth's atmosphere?
According to Wikipedia, the Ingenuity helicopter is an astonishing piece of engineering having some attributes beyond the equivalent of the classical helicopters:

The lower gravity of Mars (..) only partially offsets the thinness of
the 95% carbon dioxide atmosphere of Mars thus making it much harder
for an aircraft to generate adequate lift. The atmospheric density of
the Red Planet is about 1/100 as that of Earth at sea level, or
approximately the same as 87,000 ft (27,000 m), an altitude never
reached by existing helicopters. To keep Ingenuity aloft, its
specially shaped blades of enlarged size must rotate at a speed at
least 2400 and up to 2900 rpm, or about 10 times faster than what is
needed on Earth.

I am wondering if the research done to make Ingenuity work can be used to improve helicopters flying in Earth's atmosphere or it is solely useful for very narrow cases like flying in very low pressure? Is the special design applicable to increase the maximum altitude for helicopters flying over Earth?

Physics and aerodynamics are not magically different between Earth and Mars, so yes, everything we know about helicopters in general and about Ingenuity in particular is applicable on both planets.
You could apply the design of Ingenuity to a helicopter on Earth. You would need to make it three times lighter, of course, to counteract the triple gravity.
But the question is not so much: can we fly something like Ingenuity on Earth. The question is: what's the point of a helicopter that can fly at 27000m but runs out of battery after 180 seconds, is only the size of the palm of your hand, and can't carry any payload? It doesn't even have enough power to get up to 27000m on its own, so you need to deploy it from somewhere … but if you have an aircraft at 27000m anyway, then what do you need the helicopter for?
Helicopters are terrible aircraft. They are very complex, very inefficient, and very expensive. Their only advantage is their maneuverability in tight spaces and their ability to hover in place … but there aren't a lot of tight spaces at 27000m. And at 27000m altitude, an airplane flying in a circle is, for all intents and purposes, hovering in place compared to the ground. So there is simply no need to have a helicopter there.

I disagree until the end.  There is one use for helicopters at such altitudes--high altitude rescue.  Your circling plane can't pluck someone off Everest.  I can't see Himalayan rescue being a big enough business to cause anyone to design a helicopter to operate up there, though.  (I won't say search and rescue because there should be no search involved.)

@LorenPechtel “can't see Himalayan rescue being a big enough business” – well, Mt Everest alone has become such a popular place to go (if not popular place to die...) that I could see this being financed all by the rich people who wish to brag about having climbed up the highest place on Earth but never mind the unglamorous-but-deadly climb down.

@LorenPechtel: 27000m and Everest are two very different beasts, though. The altitude record for helicopters is already way beyond Everest, and it did not require any modifications to the helicopter other than stripping 200kg of mass (and adding oxygen for the pilot, obviously). The helicopter that was used for the record Everest landing was a stock model with only 120kg removed. You don't really need radically new engineering for Everest, just more powerful engines, maybe some partial oxidizer injection.

For reference, Mt. Everest doesn't even go up to 9 km, let alone 27 km.

@JörgWMittag Yeah, I was thinking of higher than current helicopters can go, not 27km.

"Their only advantage..." they also don't need runways, quite big advantage on Mars. They can also do short distance hops using power for only tens of seconds. I don't think a fixed wing craft could do anything useful on Mars or Titan for a long, long time, if ever.

Ingenuity is an impressive feat of engineering - its flight dynamics run on an open source Linux loop at 500 Hz, using a standard off-the-shelf processor which is way faster than other processors NASA is using.
But not so much because of its rotor speed. Rotor rpm simply scales up/down with blade length to bring blade tip speed to the optimal Mach number. At 2,900 rpm = 303.7 rad/s, the tip speed of the 1.2 m rotor is 182 m/s, well below critical Mach in Mars' atmosphere.

Photo above shows the blades of the test vehicle, which were optimised for blade stiffness and drag at low density. It is from this document, which also mentions that the rotor was designed at normal blade tip speed:

Actual Mars atmosphere conditions are significantly colder (e.g. approx -50 C), resulting in different blade aerodynamics conditions such as the Mach number. However, since the helicopter is operated with conservative tip Mach speeds (≤ 0.6), flight dynamics and performance results at ambient temperatures (e.g. approx 20 C) can be easily matched to the Mars conditions.

The altitude limit for helicopters is not so much because of the rotor design, supported by the familiar shape of the rotors in the photo. It is because of the air breathing engines powering the helicopter - even with super- and turbochargers, there is simply not enough power generated  to sustain flight. Fixed wing aeroplanes can fly higher:

They can fly faster, and compress incoming air with the ram effect.
They do not superimpose rotor tip speed on the flight speed.

Ingenuity can fly on Mars' thin atmosphere because it is powered by an electromotor, the flight tests on Earth were done at a lower weight by offloading power and avionics. The electrical wires provided power - but we cannot power an electrical helicopter with a 27,000 m extension chord.

Maybe we could power it with a directed microwave beam from a fixed-wing aircraft circling the site, or something like that?

amusing myself thinking about a miniature version you can switch on and put in your microwave oven on high and it hovers in place while the microwave is on


text:
Is a wingtip vortex strongest at the critical angle of attack?
Generally, wingtip vortices increase in strength as the angle of attack increases.  Is the critical angle of attack/Cl Max the peak strength, or do the vortices generally continue to increase in intensity once the plane is in a stalled condition? For the purpose of this question, assume the stall is not an accelerated stall and is entered from straight-and-level flight in smooth air.
If taken to an extreme, such as a 90 degree angle of attack, there would no longer be wingtip vortices, just turbulent flow and drag.
If it doesn't peak at the critical AOA, where does it peak?

Pretty sure the peak is at Clmax.  I've always thought of induced drag as the energy consumed in redirecting the air to generate lift, including the efficiency losses of air leaking around the tip, but I'm probably wrong.

Note that I think that the max being at the critical AOA/Cl Max is right and would also be my guess based on definitions. In order to learn more, I would like to see measurements. I am hoping someone may have access to aerodynamic simulation software who could generate a data graph to prove the abstract hypothesis.

@JZYL I know what you're getting at and was considering changing it already. It's fixed.

do the vortices generally continue to increase in intensity once the plane is in a stalled condition? For the purpose of this question, assume straight and level flight in smooth air

These sentences are contradictory. Never mind.
The strength of the tip vortices post-stall depends on the wing's stalling characteristics. If the inboard section stalls first (which is desirable because it helps keep the ailerons functional) then the tip vortices will continue to increase with angle of attack until the tip section itself stalls. At that point lift near the tips drops sharply and the vortices will decrease accordingly.
If the plane is capable of post-stall flight at extreme AoA, it will not be travelling fast enough for the vortices to maintain significant energy.


text:
Could a propeller system for airplanes with automatic, cyclic blade-pitch control that is designed to counter p-factor be practical?
Considering that P-factor is a result of differing angles of attack of the blades on an airplane's propeller, I would imagine that if there was a design that could control the pitch of each individual blade as it went around the arc, much like cyclic control on helicopter rotors, the thrust-line could remain centered on the propeller by a system that can measure the angle of attack and adjust the blade angles to have the same AOA during the down-swing and the up-swing.
Has this been attempted, did it work, or is it known to be an impractical design due to the high speed of these moving parts or some other reason?

Interesting idea!  The blade would be changing pitch back & forth hundreds of times each second, every second that it's running, but that doesn't mean it couldn't be done if the motivation was there.  Will be interested to see any answers to this.

Hmmm, seems like a design trade. Cost, complexity, weight, failure mode vs. not having to control it with pedal and/or yaw trim.

Large model helis' rotor rpm is close to full-scale airplane prop rpm, so high speed isn't a concern.  Aerobatic ones go up to 4000 rpm.

I bet why nobody's built one is the cost of the swashplate mechanism, and yet another control to operate (or AoA-to-gizmo autopilot to supervise) when the rudder's already good at that.

@RalphJ A regular GA prop at 2400 RPM would change pitch 80 times a second, 40 times up and 40 times down. You need to look at model airplane propellers to find ones which do it hundreds of times each second.

@PeterKämpf Fair point -- "dozens of times per second" would be a better characterization.  Still a lot of changes, and per-blade rather than all blades together as conventional props do, but not "hundreds."  Wonder what the failure modes would look like, if one blade's mechanism jammed or went astray in some manner, how bad that could be?

You should consider the other ways p-factor has been addressed in designs.  Trim tabs, mounting the vertical tail at an angle, mounting the engine thrust line at an angle, etc. are all passive means.  The AT-6 Texan II (turboprop trainer) incorporates a digital control loop of some sort to take out the p-factor -- so the novice pilots don't learn habits they won't need on jet aircraft.  It seems there are many simpler ways to do this.

Might be cheaper to just build a counter-rotating propeller than to try to design a hub that can customize blade angle based on clock position. Unless perhaps, a prop with individual electric servos within the hub to drive each blade, managed by a computer.

if there was a design that could control the pitch of each individual blade much like cyclic control on helicopter rotors, the thrust-line could remain centered on the propeller. Has this been attempted, did it work?

Yes, having a swashplate to control a propeller not only has been attempted but it routinely works pretty well on any V-22 :-)
Anyway, having the V-22 two contra-rotating and mutually connected propellers, the swashplate doesn't need to be used as you intend when it flies like an airplane rather only to control the collective pitch.
I suppose that the same system might be used on a GA airplane as well. Anyway the passive tricks already implemented to counteract the p-factor (tailplane at an angle, proper trim, training, ...) are definitely more simple, cheap and reliable than a swashplate.

So, let me try to explain two things:
P-factor or Asymmetric Blade Effect is a effect that occurs when the blade that moves downwards tend to produce more thrust its counterpart blade(blade that goes upwards).
The second explained thing is having 'Cyclic Blade-Pitch Control' which refers to the ability of changing the pitch angle of each propeller blade individually and dynamically as it rotates around the hub. It is commonly observed in helicopters to manage the rotor's thrust vector, but less common in fixed-wing aircraft.
After the explanation of these two things, we can try to consider the practicalities of this question. First, designing a system that can encompass 'Cyclic Blade-Pitch Control' needs a precise mechanical and electronic controls. This increases the complexity of the design in the present.
Second, the design must persevere the mechanical and operational stresses of flight and the complexity can cause potential for disaster or failure.
Third, there is no evidence that we have the advanced technology to achieve this control system for a commercial aircraft.
Forth, the complex design, based on this question, will be one of the most expensive designs in the history. Probably, no one is gonna take the risk of designing a complex design that needs a futuristic approach with an expensive development cost and unwarranted safety implementation.

I didn't downvote but the swashplate normally found in any helicopter and that let the blades change pitch cyclically is no "advanced" or "futuristic" technology

I'm not sure how you go from "common in helicopters" to "one of the most expensive designs in history". Did you use generative AI to write this answer?

1, For sophit: The swashplate's normally found in any helicopter, as you said, is common for helicopters, but when it comes to commercial aircrafts or other developed aircrafts, its use in the aircraft's design is gonna ask for a lot of mechanical and electrical effort. For Sanchises: The design for a helicopter and a commercial aircraft differs in many things, and I wanted to mention the swashplate's unwarranted usage in the aircraft, considering how difficult it is to implement it in a normal aircraft(excluding helicopter). I used what I read + critical thinking, for your knowledge.

Why should the mechanical and electrical effort be higher than in a helicopter? Propeller blades are generally much lighter and generate much less thrust than a helicopter one, the opposite might actually be true...

FOR SOPHIT: The mechanical and electrical effort can be higher than a helicopter since I was referring to commercial aircrafts. It's obvious that commercial aircrafts need more force, thus more effort.

Helicopters are commercial aircraft... The biggest "effort" of a swashplate I can thing about is the one of the MV-22 and it seems to work pretty well.


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What jet is this?

Anyone have any idea what jet is this? From the picture it seems to British and it also looks like it's from the 1950s or 1960s. But other than that I couldn't identify the type.

It is actually the third prototype which flew first in 1947!

I thought I left a comment here containing information explaining how to get the answer to such questions.

That is a de Havilland DH108, which is possibly most notable for the crash that killed its pilot, Geoffrey de Havilland Jr., son of the founder of de Havilland Aircraft Company.
Only 3 prototypes were ever built, and all three crashed.

It does resemble the German me163.

@WenHuiWong ... but was even more lethal to its pilots. All three prototypes crashed.


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Six Propeller Engine Military-Type Aircraft at KPHX Sky Harbor
I was browsing the Google Maps 2023 image of the now-demolished Terminal 2 at Sky Harbor in Phoenix, Arizona.  (See below.)  I noted what appears to be a six-engine military transport aircraft parked in a spot that used to be the terminal gates.  It looks at first glance like a six-turboprop C-130.  But the engine spacing is odd.  The odd spacing could be a result of photographic distortion.  For that matter, the six engines could be the result of distortion.  The wing has an ID of what appears to be C38 or C39.
Anybody know what this is?  Many thanks from a brand new newbie.

That looks like a computer generated image...

Indeed it looks computer generated, or an artifact of an image glitch.  Here is a link that should take you to the spot.  https://www.google.com/maps/@33.4343565,-112.0175681,85m/data=!3m1!1e3?entry=ttu

Scroll right and look at other images of swept wing commercial jets, there are similar anomalies.  My guess is that Google is applying some AI to "clean up" the edges of blurry raw images, and that it mistook wing mounted fuel tanks for engine nacelles and applied the programed enhancements by adding a propeller to make them look more "real" without knowing there are only 4 engines.  Isn't technology great?!

It seems recently Google has started baking their "AI enhancements" from their 3D view feature into the raw image tiles. Expect much more of these artifacts in the future: https://mt0.google.com/vt/lyrs=s&x=396025&y=841707&z=21

It's completely commonplace that google maps does this sort of "slightly incorrect image tiling".  You can trivially find innumerable examples by opening a browser.  It's a total commonplace of everyday life for some years now.  It's sort of surprising someone would ask a question about it!   (Note that simply in the very same image there are any number of other "slightly incorrect tile joins" and the other obvious slight imperfections you see constantly and everywhere street view and street overhead-view.

Aircraft without engines, C-130 with jet engines, neglected 737

@AdityaSharma - The C-130 appears to just be missing it's propellers, which is plausible considering that it is parked 2,400 feet from the boneyard. And the engine shadows seem to match this, although the engine shadows on the right wing are from a different Sun direction than the rest of the plane (stitching together different days maybe?). But look at the shadows of the three nearby C-130's, the propeller shadows seem outsized, in fact the blades look like they would be hitting each other. Perhaps the shadows were enhanced by AI for clarity?

Here's another example: 33.915550,-84.509017

You can see two C130's on the hard stand at Dobbins ARB in GA, next to the Lockheed facility.  The one pinned above looks like they edited turbofan engines instead of turboprops.  I agree they did the same with the external fuel tanks in the original post. Somebody at Google needs some help.


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Does FAA class 1 medical require binocular vision?
Can I get an FAA Class 1 medical if I don't have binocular vision?
I live in Italy and for EASA I can't get my first class medical certificate to be a pilot.  But can I get at least FAA 1 class to be a pilot in USA?

Yes, with a special issuance, and provided you meet the criteria here you can get an FAA class 1 medical with monocular vision.

An applicant will be considered monocular when there is only one eye
or when the best corrected distant visual acuity in the poorer eye is
no better than 20/200. An individual with one eye, or effective visual
acuity equivalent to monocular, may be considered for medical
certification, any class, through the special issuance section of part
67 (14 CFR 67.401).


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Why is icing more critical on smaller airplanes?
My professor mentioned that the contour of smaller airplanes changes more drastically than that of larger airplanes. In this context, he mentions the surface-to-volume ratio. But how does that relate to the more drastic change in a small plane's contour?

A comment because it addresses the title, but not the body of your question (which is answered below).  Large aircraft tend to have more climb performance, spend less time at "icing altitudes" and have hot engine bypass for deicing.  All make icing less critical than on a propeller general aviation aircraft.

I think your professor simply meant that 1m of iced leading edge on a wing of 80 m span has a different effect than on a wing of 8 m span

Another comment to address the title, many small aircraft (read GA) simply don't have de-ice equipment so getting caught in icing can quickly become fatal.

Had a bit of a confused moment reading this on HNQ because I thought this was a Seasoned Advice question ...

There'a value when discussing airframe icing called "collection efficiency". It's the proportion of supercooled droplets in given package of air that will penetrate the boundary layer of air and strike the surface instead of being carried around in the boundary layer.
Collection efficiency increases the smaller the leading edge radius is; that is, a sharp leading edge shape will collect more droplets in a given package of air. So it means smaller radiused flying surfaces and other shapes tend to collect more of a given volume of droplets than a blunt one of the same overall size.
The other factor is the total volume of supercooled droplets relative to the wing, and their ability to modify the airfoil contour. A very large wing is modified way less by ice accumulation for a given water droplet density, so it can tolerate more accumulation.  The A-380's inboard leading edge is so large and with such a blunt radius, it doesn't need anti-icing at all.
On a side note, lots of jets don't use any anti-ice on the horizontal tail, because they basically over-size the surface so that it can generate minimum stability and trimming/control forces when loaded up with ice. When ice free, it's actually much larger than necessary.

This is effect is clear when one sees ice formation on an aircraft.  If you are trying to see if there's ice forming it's best to look at small radius items such as the temperature probe that sticks through the windscreen on a small aircraft.  That will show ice before the wind screen itself.

The ice accumulation makes the radius even smaller, causing even more accumulation, and you end up with that wedge of rime sticking out. In the CRJ, we were supposed to get out of icing if accumulation on the cockpit side windows was happening that the internal heaters couldn't cope with.

Icing is critical on all aircraft for 3 major reasons.

Loss of lift
Added weight
Increased drag

If we took an airfoil and scaled it down to 1/10th its original size, the contours are the same, but the professor is right because the Reynolds number will be different.

Reynolds Number = Chord x Velocity/Kinematic viscosity

Smaller aircraft generally have smaller chords and lower airspeeds.  Relatively, the ice build-up will change the contour of the smaller wing more.  But there is more to the story.

higher airspeed delays onset of turbulent airflow.

The second effect here is that less energetic airflow of the smaller plane will tend to separate earlier (even without icing).  This can be seen on the Airfoil tools website with various Re numbers. They have a wide selection of airfoil types to study.

Another perspective:  The “usual suspects” for why airframe icing is a problem are lift reduction, weight, and drag.  As with many things about wings, that oversimplifies things…  we’re misunderstanding the most significant danger to airframe icing.
By changing the shape of the airfoil and the airflow over it, you are moving the location of the CL (center of lift) and altering the angle of the lift vector as well.  You may be producing enough lift, and little drag, and adding little weight, but unknowingly be changing pitch stability about the lateral axis outside of design parameters.
Small planes have surprisingly small CG envelopes of just a few inches whereas a transport category plane may have a significantly larger CG range.  A Cessna 182 at gross weight has a CG range of 5” or 127mm.
In a fully loaded light aircraft I will often only be an inch or two from one of the CG limits.  That means a 1” change in the location of the CL will put me out of envelope.  And even more, I will likely be accumulating tail ice, which is a huge and under-estimated problem.  Large transport aircraft rely on stabilizer trim, not elevator trim, giving them much more trim authority, thus more CG range, hence more options to adjust to a CL affected by ice accumulation.
What we may believe is a loss of lift, is actually a loss of sufficient elevator authority required to maintain an angle of attack that leads to level flight…  and that lack of authority may be because icing lengthened the CL-CG arm, or reduced elevator downforce effectiveness, or both.
Some icing problems, like frost accumulation on the ground, will affect planes proportionally to their size.  But aerodynamic icing in flight puts the aircraft with a smaller CG range and less pitch authority at much greater risk.  Making matters worse, a “smaller” aircraft often has less climb capability (excess power) and a much lower ceiling (un-pressurized, less power, wing design, lack of turbocharging, etc) so we often can only descend out of an icing layer, not climb out of it.  This cuts our escape options in half and requires us to descend back through the conditions that accumulated the ice if we were climbing.
So when we say “smaller” aircraft are more susceptible, “smaller” actually means airplanes with a narrower CG range, and/or less excess power, and/or less elevator/trim authority.

Additional reading here


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Why do you think the 747 extended downwind to 6 miles?

Why the 747 extended downwind to 6 miles?
Why do you think Horizon turned 90 degrees to join the final?
What is the “rule” regarding Visual Approaches?

Not to be rude, but how do you expect anyone to provide an answer to what appears to be a specific incident if you don't provide any context or details?  Is this something you saw on Flightaware?  Is there a YouTube video, or incident report that is at the origin of your question?  We like to be helpful here, but you need to help us help you!  ;)

I doubt the horizon turned 90 degrees in a 747! Normal bank is 30, max. is 45!

@Bianfable, oh... I interpreted that as a separate Horizon airlines flight turning for 90 degrees of heading change.  Because we have Horizon airlines up here in the NW.  And because it was capitalized i assumed it was a company name...  (given the quality of the question I probably made the wrong assumption!)

@MichaelHall I didn't think of Horizon Airlines, maybe you're right :) That makes one more thing OP should clarify...

For sequencing.

Because it was on a 90 degree base leg.

Look outside.


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How to pass ATPL as an ATC?
i have graduated from Nation Aviation Academy and my occupation is Air Traffic Control. But to become a pilot was my childhood dream. So my question is, is it possible to pass atpl exams in this situation or is it necessary to pass the pilot course? I already have medicine and icao level. Thanks in advance for answering my question.

You can't just skip PPL and CPL to become ATPL. What do you mean when you say that you have "medicine and ICAO level"?

I have medical certificate class 1 and English level 4 i meant that. So can i pass PPL and CPL as an ATC?

You can take the PPL and CPL courses without an ATC. The "ATC" part has no bearing on your quest to get an ATPL, it doesn't allow you to bypass anything.

I meant that i am ATC, is it enough to pass PPL or CPL without any course? is my background enough for just passing exams but not taking course?

I doubt it. You'd probably ace the airspace and weather stuff, but there is a lot of other things in there. Plus you need an instructors endorsement or certificate of graduation from a course to take the tests. BTW, just passing the course doesn't mean you get a PPL or CPL, you still need experience requirements and check rides.

thank you for helping

If your only goal is to take the written test for personal fulfillment I can't imagine a commercial test facility would refuse to take your money.  As others have pointed out, this won't get you an ATPL, just a passing written test score.  (if you can pass...)  I might be wrong, but I don't think an instructor endorsement is a hard requirement just to have a go at the written.

Welcome to aviation.SE! Are you asking about a specific country? Regulations and licensing can be very different in different places. Being a controller would certainly help with some things, but ultimately you still have to learn how to fly an aircraft.

@MichaelHall Most test facilities will not allow you to take a test without an instructor endorsement. You can find practice tests online if it's just "personal gratification", but anything that is official requires official process.

Thanks Ron.  Just sayin' though, if it ain't prohibited by CFR, cash talks!  ;)

A Google search for "Nation Aviation Academy" does not find anything. Please tell us which country are asking about.

@MichaelHall - Part 61.35 does require an instructor endorsements. CATS/PSI locations in my area will not let you sit for the PPL, IR, or CPL without endorsements. You can get around that by taking one of the many online courses available. They will send you a pdf endorsements to take to the testing center. Here’s the catch. You can take the BGI, AGI, CFI, and CFII without endorsements. And, the question banks are nearly 90% identical to the tests that require endorsements.

Thanks for the reference Dean!

Being an Air Traffic Controller does not provide any legal shortcuts for piloting courses, in any jurisdiction as far as I am aware. Sure, you could probably sleep through the lectures on meteorology and maybe parts of others, but you still need to sit and pass all 14 exams. You would have little to no advantage on the subjects of aerodynamics, aircraft systems, performance and loading, and human factors.
You also need to complete the practical flight training and meet the same requirements as everyone else.


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Is this free flight data really correct?
In recent years, I'm being terrorized by airplanes flying over here all the time at low height. For this reason, I'm trying to set up a little notification system to see if these are actually "official" aircraft, and if so, who owns them and when they fly over here. Basically, I want to be able to verify on my screen that yes, that loud noise from the sky is indeed an actual commercial (or at least "registered") aircraft, and not just my imagination or worse.
So, for this reason, I've been hunting for free flight data. That is, the current GPS coordinates for all active airplanes in the world. (Or at least around my area.)
Unsurprisingly, there's eight million companies/websites out there which provide this data, but want to get paid, or have annoying registration requirements.
Eventually, I found this: https://opensky-network.org/
I started reading its manual: https://opensky-network.org/apidoc/rest.html
And found out that they do allow unregistered people to fetch their data here: https://opensky-network.org/api/states/all
However, studying the output from that JSON blob, I notice that, currently, it only contains 2482 "states", a "state" apparently meaning an airplane in the sky. And only one out of all those is said to be from Sweden.
Does this really mean that only 2482 airplanes are in the sky right now in the entire world, and that only ONE airplane is in the sky over Sweden? Or does the origin country label ("Country name inferred from the ICAO 24-bit address.") mean from which country the airplane is "owned"/based? Or where it started from for the current flight?
Whatever it means, 2482 airplanes sounds a bit low to me. Could this really be accurate? And if so, if this website can give it away for free, how can the others charge so much money for it?

@quietflyer Had you bothered to actually read my question, there would be no doubt about what I asked. That you would latch onto this detail and ignore my question shows me that you are one of the many people out there who have zero intention of helping. Thanks for the downvote, BTW.

@landcrab I've tried to address some of your questions in my answer below, but you are likely to get a better response if you avoid emotive terms and exaggerations in your question and focus on the things you really want answered.

Do you live near an airport?  And perhaps there is a communication issue with English not being your first language, but if you are feeling terrorized and are having trouble determining whether the aircraft flying over your house are real or imaginary, ("or worse" as you said!) I might recommend that you seek professional counseling.

I'd suggest finding out what the closest airport to you is and looking up their approach and departure plates. It's a little difficult to me (a non-pilot) to relate those to a "real world" map, but I'm sure some here would help you overlay that with your local town. It may simply be that you're on the approach or departure path for your local airport.

You can first check four opensky receivers in your area. This post on their network tells how to do that. It does sound like you might be situated under an approach or departure path for a nearby airport.

As Freeman says, if you want to say what airport you are close to I would be willing to make a kml file to translate the plates into actual map data.

The flight data provided by the various aggregators, including the OpenSky Network is gathered by volunteers operating ADS-B receivers at their own expense. OpenSky had about 1100 receivers on line when I looked, covering predominantly Europe and the US (FlightRadar24 claim 13000 and use other sources as well.)
The range of ADS-B transmissions is limited by geography and altitude, so unless there is a receiver within range the aircraft won't be recorded. That range is limited to a couple of hundred miles or so but an aircraft at low altitude, or flying over hilly or mountainous terrain will only be picked up at much closer ranges.
Additionally, not all aircraft are required to carry ADS-B equipment.
So, your figure of 2482 aircraft seems reasonable for the area covered by OpenSky.
You haven't said where you are, but it's quite possible that you're out of range of the nearest OpenSky volunteers. If so, OpenSky won't help you.
You'll have more success with a commercial organisation like FlightRadar24 or FlightAware, but if you don't wish to register that avenue is closed to you. Even so, non-equipped aircraft won't show up.

If OP is really out of range of the nearest receiver, they could also set one up themselves (OpenSky - Improve Coverage).

@Bianfable True, but if the OP won't pay for access to, say, FR24, they're not likely to want to fund a receiver.


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Are the gyroscopic precession and P-factor of a pusher propeller in opposite directions?
according to this picture

the P factor cuases airplane to yaw to the right but if pilot wants to pitch up , then p factor and gyroscopic precession acts on airplane at the same time but in opposite direction if propellers rotates counter clock wise in such manner : p factor makes the airplane to yaw to the right but gyroscopic precession makes the airplane to yaw the left
is that true?
sorry about my poor english language

That would be correct, as you can see from this video on Veritasium Youtube channel
Mind you, the pecession would only affect the plane for as long as it is rotating. P-factor is dependent on angle of attack, which of course would increase during pull, but when rotation stops, the "precession force" stops, and P-factor remains.

that means they cancel each other? what's the effect of side slip on p factor?

Precession is not, if I reacall correctly, mentioned in pilot training, so it must be negligible. I'm guessing P-factor is at least an order of magnitude greater. Sideslip would have some effect. In this case, flying "left side first", it would push the nose down.

They may cancel each other in a  transient condition, but only while yawing/pitching.  Side slip will change the P factor's orientation somewhat, to the extent that the airflow has changed relative to the propeller axis.  Say the flow is now coming from 7 o'clock due to side slip instead of 6. The P factor force orientation should move from 3 o'clock to 4 o'clock during the slip, to the extent that you have power on during the slip.

@Jpe61 precession forces can be much stronger, as you discover if you raise the tail of your C-180 very quickly on takeoff. and the nose swings hard from precession, but that's a brief transient state anyway.

My takeoffs were always silky smooth, so never noticed that

@john k when an aircraft yaws to the left this means that relative airflow now coming from the right (negative yaw and positive side slip), in positive side slip , which part of propeller disk have greater thrust? right side of propeller or left side? can you describe this in details?

@alireza The part of the disc with the greatest thrust is 3 o'clock looking from behind because the blade passing 3 has the highest angle when the prop axis is at a positive angle to the airstream. If you are slipping to the left, that is left wing down, with a positive AOA, the relative airflow goes from straight on from below, to offset to the left from below; 6 o'clock to 7 o'clock.   The propeller disc sees its maximum blade angle shift from perpendicular to 6 o'clock to perpendicular to 7 o'clock, or from 3 o'clock to 4 o'clock. In that case P factor would create a slight NU tendency.

@JohnK in alizera's example the rotation of the propeller is opposite to "normal", as it is a pusher, the blade going downwards would be the blade at 9 o'clock.

So I think the effect is 180 degrees different?

Yes you just flip it right to left.  3 o'clock becomes 9 o'clock.

thank's a lot my friends

They depend on different things. Gyroscopic precession occurs when you change the propeller's attitude- it causes a yawing tendency to the left when the counter-clockwise propeller is pitched up and to the right when it is pitched down. How big this effect is depends on how abruptly the pitch is changed.
P-factor depends on the current angle of attack of the propeller blades. Typically the plane is flown so that the descending blade has a higher angle of attack than the ascending blade, which causes it to produce more thrust. This causes a yaw to the right for a counter-clockwise propeller.
So both gyroscopic procession and p-factor can be in the same direction in some occasions. For instance, if the nose and angle of attack are initially high and they are quickly lowered, then both gyroscopic procession and p-factor will be to the right while the nose is being lowered.